Tuesday, 21 July 2009

Land of the Dodo 11: Weaving a spell

Scattered through Madagascar and the nearby islands of the Indian Ocean is a group of at least 10 species of weaver birds, the fodies of the genus Foudia. Unlike the colonial weavers of mainland Africa, they behave far more like most passerines, nesting in paid by themselves.

Primarily forest birds, one species, the Madagascar or Cardinal Fody, has adapted to open grassland and is often found around farmhouses. As a result of people liking their colours, the Madagascar fody has been taken to many other islands, including St Helena in the Atlantic.
At first contact, there were three fodies in the Mascarenes, one for each of the islands, but today only the Rodrigues fody F.flavicans (left) and the Mauritius fody F.rubra (top)survive. Even these only barely managed to hang on, with the Rodrigues at one time down to perhaps 6 pairs before conservation measures helped its recovery (it currently stands at 900-1000 birds). The Mauritius fody is in far worse shape, and there are intensive conservation measures being undertaken to help it to survive.

Fodies are most closely related to the Orange Bishop, Euplectes, an African weaver bird that like the fodies nests independently. One might think that the birds on the islands originated from Madagascar, but analysis of their DNA shows that the sequence runs from the Seychelles, then to Rodrigues, then Mauritius, and finally Reunion, Madagascar, and the Comoros islands. Originally a rainforest bird, one of the Madagascan species adapted to grassland, later became a bird of farmland, and has now been introduced to all three islands, which on Mauritius and Rodrigues it shares with its close relatives.

The main cause of the decline of the fodies was probably introduced rats, which readily predate fody nests. It is one of the ironies of conservation that the only reason the Mauritius fody survived was because of aplantation of introduced Cryptomeria trees, which do not provide food for rats or monkeys and consequently enabled at least some nests to escape.

Intensive help for the fody, and indeed the other passerines of Mauritius, only started in 2002. Fodies have proved reasonable straightforward to breed in captivity, and techniques of hand rearing have been devised to enable chicks from wild nests to be reared. This is of course a very labor intensive process, and readers may be interested in the rearing diet. This comprised the following:
Bee larvae (throughout the rearing period)
Crickets (first guts, then abdomens)
Waxworms (older chicks only)
Mice (first internal organs, then cut up as the chicks grew)
In addition, chicks received Nutrobal, Avipro, and Nekton as vitamin and mineral supplements

Initially chicks were fed hourly between 05:00 and 21:00, with the intervals between feeds increasing to 2 hours by the end of the rearing period, with chicks fledging at 18 days. Hand reared chicks were kept in a brooder at 36 degrees at first, gradually reducing as they fledged to the ambient air temperature of 26 degrees.
These hand reared chicks were released on isle aux Aigrettes, and the attempt has proved a great success. Fodies are now breeding on the island, with over 150 birds. One problem is the introduced Madagascar Fody (below), which could potentially hybridise. It appears however that the difference in preferred habitat and song make it unlikely for the two species to interbreed, but the situation is being closely monitored.

Mauritius Fody image from Durrell Wildlife
Rodrigues Fody from ARKive
Madagascar Fody from Wikipedia

Monday, 13 July 2009

Is it a mouse? Is it a deer? No – It’s the Mouse Deer!

Tucked away in Twilight World at Bristol Zoo, and all too often overlooked, is one of the smallest of the world’s hoofed animals, the Lesser Malay Mouse Deer Tragulus javanicus. Only about half a meter long, and weighing about 2kg, it is an inhabitant of south east Asian rainforest and scrub, often close to water – basically anywhere they can find dense cover.

Technically, the common name is something of a misnomer, as it is actually not a true deer, but a chevrotain belonging to the family Tragulidae, which is close to the base of the group of hoofed animals called the artiodactyls or even-toed ungulates, which also contains the pigs, hippopotamuses and giraffes, and which is now thought to be the group that gave rise to the whales. Their fossil record dates back to the Miocene in Europe (c15mya), but they had a long record before then, as the earliest whales are known from Eocene rocks of 47.5 mya, and mouse deer must have branched off the group which gave rise to them much earlier – probably just after the end of the Cretaceous period when non-avian dinosaurs became extinct, if not earlier.

As primitive ruminants, mouse deer lack many of the characteristics of more advanced forms – for example the main form of male display is by enlarged canine tusks rather than antlers or horns. The stomach is fairly simple, with only three chambers compared to the four of deer or cattle, and all in all they bear a surprising resemblance to the agoutis of South America, which are of course rodents. The diet is mainly vegetarian, especially fruits, although they do eat snails and some insects as well, and they probably also take fungi.

They reach maturity quickly – usually within a year but they have been known to breed at six months. They have one or two young at a time as far as is known, but they have four teats, which may indicate they sometimes produce larger numbers of offspring.

There are several other species of mouse deer, of which the commonest is the Greater Malay Mouse Deer Tragulus napu. There are also mouse deer in India, and also a more distantly related form in Africa, Hyemoschus.. It is very likely that more species are to be described – with such a huge range and antiquity of the group, there are probably several cryptic species included in the described forms. This makes things very difficult for zoo conservation, as unless you are careful to breed only animals from a known geographic location there is a strong risk of producing hybrids which have no value for conservation purposes.

As “bite sized” animals, mouse deer are understandably nervous creatures, but they tame quite easily – in Thailand they are often kept as pets in the back garden. They figure prominently in folklore – Mouse Deer is a trickster figure like Brer Rabbit who triumphs by outsmarting anything that wants to eat him – which is everything!

The chief threats they face today are hunting and habitat destruction. Their status in the wild is very little known – as nocturnal, secretive animals they are very hard to study. The only Mouse Deer that are likely to be seen in zoos outside Asia are the Greater and Lesser Mouse deer. European zoos have concentrated on the Lesser Malay, whereas American zoos have concentrated on the Greater Malay - this ensures that there is less duplication of effort. There have been efforts to encourage the expansion of the European zoo population of Lesser Malay mouse deer – Bristol Zoo currently has only one pair but has successfully bred them in the past and distributed them to other collections. According to ISIS the current European zoo population stands at 44 animals, with 9 births in the last year.

(Photo from Wikipedia commons - ignore the eye shine)

Friday, 3 July 2009

A Tale of Two Squirrels

The commonest wild mammal now seen by the average person in the UK is an introduced species, the Eastern Grey Squirrel Sciurus canadensis. Introduced in the late 19th century to England, it spread rapidly from the first. It has widely been blamed for the decline of the Red Squirrel Sciurus vulgaris, and practically no one has a good word to say for it.

However, the true picture is a bit more complex. For one thing, practically all the Red Squirrels in the UK are themselves the result of reintroductions from mainland Europe, which began in Scotland as early as 1772!

Our original Red Squirrels were probably an endemic race of the widespread Eurasian Red Squirrel, which has a huge range in Europe from Norway to Spain, and east as far as Greece. In the Middle East it is replaced by the very similar Persian Squirrel, whose only European station is on the island of Lesvos, which is in sight of the Turkish coast.

The Red squirrel is primarily a conifer specialist, in the south being found in stone pine woods around the Mediterranean and at altitude in the Alps. It can survive in deciduous forest, where it depends heavily on Hazel. In addition to seeds, it will take birds eggs, the buds of trees, and bark. However, in Oak woodland it is at a disadvantage, as it has trouble digesting acorns.

Red Squirrels reached Britain at the end of the last Ice Age, when the tundra that had covered southern Britain was replaced first by Taiga forest of Birch and Pine, then in turn by mixed deciduous woodland. Even after the Channel formed and Britain was isolated, squirrels would have been fine in the oak forests that covered England, especially along rivers where the activities of Beavers would have encouraged Hazel coppice.

The squirrels’ troubles started when Neolithic farmers arrived and began clearing the woods for farmland. The deforestation was quite rapid – by the Roman period the proportion of forest cover in England was about the same as today – but the habitat loss was inexorable. By the 18th century the demands of a growing population and the building of the British Navy had reduced tree cover to perhaps 2% of the country, and even in Scotland few if any remain – the last in Sutherland was reported in 1642 for example.

The needs for the British navy to have a source of timber for shipbuilding then caused a swing in the squirrels favour. As well as new plantations of conifers made by landowners, they introduced Red Squirrels. Some of those were moved from other parts of the country, but there were also imports from Scandinavia.

It is in this context that the Grey squirrels were introduced. As primarily animals of deciduous woodland, and with few predators (Pine Martens, Foxes, and most birds of prey having been wiped out or restricted in numbers by gamekeepers) they had a built in advantage, as they have no problem feeding on acorns or indeed anything else. In addition, they seem to carry a parapox virus which Red Squirrels are susceptible to, and as a result it seems inevitable that, at least outside the Highlands and some offshore islands in the south that they have not reached (The Isle of White and Brownsea island for example), they will continue to be the typical squirrel of Britain.

There may however be a chink in their armour. In areas at the edge of their range in Scotland they appear to be at a disadvantage compared with Red Squirrels when faced with predation by Pine Martens. These were wiped out over most of their range in the UK, but are now starting to make a comeback. Grey Squirrels are more terrestrial than Reds, and are easier for Pine Martens to catch. As a result, in areas with healthy Pine Marten populations, Grey Squirrels seem to decline, if not actually die out.

The status of Pine martens in England is unclear. They certainly seem to be extinct in the south east, but in Wales, possible Cornwall and the Lake District it is possible small populations survive. Reintroduction seems unlikely in the near future, however in the north of England Scottish Pine Martens seem to be re-colonising naturally. If you see a Pine Marten, they are quite unmistakeable –good luck on your search!